The present invention generally relates to a portable life support system and, more specifically, to an improved portable life support system using a solid adsorbent bed for the containment and generation of pneumatic and metabolic oxygen and a cold copper wire mesh for the collection and storage of expelled carbon dioxide and moisture.
Space missions often require the need for extravehicular activities (EVA) where the astronaut is placed in the non-atmospheric conditions of space. A life support system is therefore required to sustain the astronaut. Portable life support systems (PLSS) have been designed to allow an astronaut to perform EVA. The PLSS sustains the astronaut through supply of pneumatic pressure and metabolic oxygen, and a heat sink to remove metabolic heat generated by the astronaut during the course of the EVA. Because the astronauts prepare, operate and regenerate the PLSS in the zero gravity conditions of space, a need arises to minimize complexity of the PLSS so that service and maintenance by the astronaut can be easily accomplished. Also, the nature and criticality of space missions require a high degree of safety and reliability for an unlimited number of PLSS life cycles. Furthermore, to make the EVA less cumbersome and more easily performed, the PLSS must be lightweight and compact.
Both high-pressure gaseous and liquid oxygen delivery systems have been heretofore suggested. These systems satisfy to a varying degree many of the needs described above. For example, a heat sink apparatus to remove metabolic heat from an astronaut and to provide space suit cooling is described in U.S. Pat. No. 5,092,129 by Bayes et. al. This invention removes heat from a cooling medium by passing the cooling medium from a spacesuit liquid cooling garment to a heat sink assembly having a heat transfer means and a material for absorbing the heat. The heat transfer means is a thermoelectric array that acts as a heat pump. The heat from the cooling medium is pumped into the material, which isothermally changes phase. Heat is thereby removed from the liquid cooling garment. The system utilizes electrical energy to control the rate of heat rejection to the radiator surface. One of the disadvantages of this system is the consumption of electricity during EVA. The system also does not provide for all the requirements of a complete life support system.
U.S. Pat. No. 5,361,591 by Caldwell describes a portable life support system that provides both temperature regulation and breathable atmosphere using cryogenic technology. Liquid oxygen is freely stored in a dewar for use in this system. Disadvantages with this system include the fact that small quantities of heat are required, such as 92 BTU/lb, to vaporize the oxygen. The heat of vaporization is directly related to the efficiency of the PLSS. Furthermore, a complex system of valves, regulators, heat exchangers and control systems are necessary for proper delivery of the gaseous oxygen. Also, a permanent magnet must be incorporated in the dewar to contain the liquid oxygen and prevent its escape in a zero gravity environment. A separate scrubber is required to remove the expired carbon dioxide, moisture, and perspiration. Such a system adds weight and complexity to the PLSS.
A mixed gas storage and delivery system is described in U.S. Pat. No. 6,089,226 by Gier. Here, mixed gas is expelled from a compact lightweight dewar. Heat exchangers, in association with the dewar, maintain the gas therein in a single phase and provide the needed expulsion energy. Some of the disadvantages with this system are that the mixed gas must be stored at high pressure, such as in excess of 1000 psi. The high-pressure storage presents a considerable safety hazard to the occupant and the handler. A dewar and associated valves, regulators, heat exchanger and delivery system must be of high strength to store, regulate and deliver the mixed gas under such pressure. The heat sink capability of the supercritical mixed gas appears to be less than optimal. It is also not clear that the supercritical storage system provides a breathable atmosphere and removes the bulk of carbon dioxide and water moisture and stores the products for subsequent reclamation of same in the habitat.
As can be seen, there is a need for ease of servicing and maintenance of the PLSS in space. The PLSS must be serviced at the end of each EVA in a relatively short time so that it may be available to support a crew for subsequent EVAs. Use of solid adsorbents for storage of oxygen could be a major step toward simplifying and reducing the maintenance requirements. Since solid adsorbents are capable of many adsorption/desorption cycles, maintenance is virtually eliminated with their use in the PLSS. A solid adsorbent dewar also could simplify the system by eliminating the need for many of the valves, the heat exchanger, transducer, and other tubing and fittings required in current systems. A dewar construction would be adaptable to the design of a simple cluster for containment of oxygen supplies. Collection and storage of expelled carbon dioxide and moisture could be collected for subsequent regeneration and reclamation in the habitat. A cooling system, generated by electrical power, could be simplified by a system that uses ice packets in its stead. With such a system, thawed ice packets could be easily removed and replaced with refrozen ice packets in the habitat between EVAs. The ice packets could contain Velcro in select areas so they could be installed in intimate contact with the item needing heat sinking. Furthermore, thawed ice packets will be easy to handle in a zero gravity environment. Being durable and refreezable, the ice packets could be used repeatedly without loss of water.
A portable life support system using a solid adsorbent material for storing oxygen at cryogenic temperature comprises a primary oxygen supply having a solid adsorbent bed made of a molecular sieve for containing and desorbing oxygen therefrom upon the presence of heat; a liquid cooled garment, being part of a pressurized garment assembly, including liquid circulating pipes therein for conductively transferring metabolic heat from an astronaut; a liquid cooled garment loop for circulating the liquid in the liquid circulating pipes away from the liquid cooled garment; a heat sink assembly containing ice therein for conditioning the desorbed oxygen and absorbing metabolic heat from the circulating liquid of the liquid cooled garment loop; and a ventilation loop for piping carbon dioxide and moisture exhaust from the astronaut to a breathe out collection and storage device, which provides desorbed oxygen for use as metabolic oxygen and pneumatic pressure for the astronaut""s spacesuit.
It is thus an object of the invention to conserve vital resources and thus provide a simple, regenerative method for controlling the rate of heat rejection without the need for consumption of electricity during EVA. The present invention operates to control the heat of the astronaut through a simple ice cube heat sink. A temperature control valve provides the comfort desired by the astronaut. The ice cube heat sink does not consume electricity during EVA and ice packets used with the ice cube heat sink can be refrozen in the habitat and reused.
It is another object of the invention to reduce the complex system of valves and regulators currently needed for converting LOX to gaseous oxygen and to increase the efficiency of converting oxygen to a state where it can be used for cooling and consumption. The present invention provides simplification and efficiency by using a simple canister of solid adsorbent molecular sieve or carbon molecular sieve (CMS) to store the charge of oxygen needed for the EVA. The heat of vaporization of LOX is 92 Btu/lb versus 211 Btu/lb for desorbing oxygen from the solid adsorbent, thus the solid adsorbent pack is much more efficient. CMS has been demonstrated in laboratory to hold 73 wt/wt percent at minus 183 degrees C and is estimated to hold as high as 90% with further development and test. The canister is plumbed in series with the ventilation loop where moisture, CO2 and metabolic heat is transported to the canister. The return gases from the astronaut containing moisture, CO2 and heat are adsorbed in the solid adsorbent. The heat of adsorption gases causes the oxygen to be desorbed from the solid adsorbent. The desorbed oxygen provides a fresh dry source of breathing gas to defog the lens on the helmet. Since the oxygen is dry the sensible heating required to raise the gas to the comfort zone in the electrical comfort heater is minimal. In the event the heat of adsorption of CO2 and moisture is insufficient to release enough oxygen, only 15 watts of electrical energy (in the form of a battery operated electrical heater) is needed to release 0.165 lb/hr of oxygen, the amount needed to satisfy an average metabolic workload of 1000Btu/hr.
It is yet another object of the invention to eliminate the need for high-pressure storage, which presents a considerable safety hazard to the occupant and the handlers. The need for storage of supercritical cryogenic oxygen at high pressure is eliminated through the use of a solid adsorbent bed.
It is still another object of the invention to reclaim and reuse the carbon dioxide and moisture exhaust from the astronaut. The present invention provides a collection and storage device, maintained cold, for collecting and storing the carbon dioxide and moisture as an iced clinker. The collection and storage device is removable from the PLSS so that the vital elements contained in the clinker can be reclaimed aboard the habitat.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.